chapter 23 outline
chapter 23 outline BIOL 1110
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This 4 page Class Notes was uploaded by Caitrín Hall on Tuesday January 26, 2016. The Class Notes belongs to BIOL 1110 at University of Connecticut taught by Bernard Goffinet in Summer 2015. Since its upload, it has received 18 views. For similar materials see Introduction to Botany in Biology at University of Connecticut.
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Date Created: 01/26/16
Gymnosperms, the First Seed Plants 23.1 Gymnosperms include several modern groups and diverse extinct forms Vascular plants that produce seeds but not flowers or fruits Cycads – beautiful, tough foliage; ornamentals; produces seeds in conspicuous cones Ginkgo biloba – attractive and pollution-resistant foliage; fleshy- coated seeds Gnetophytes – phylogenetically embedded within the conifer clade Conifers – pine and other woody trees/shrubs that produce pollen and seeds in distinctive cones 23.2 Gymnosperms produce ovules and seeds in cones, rather than within fruits “Naked” seeds – not enclosed in fruit; produced on surface of leaflike structures (sporophylls) aggregated to form cones Lack ovary from which angiosperm fruits develop Seeds – reproductive structures that develop from structures known as ovules, after egg cells have been fertilized Ovule – integument-covered megasporangium Heterospory o Two types of spores produced by meiosis o All seed plants and certain seedless plants o Tiny microspores and large megaspores o Key to origin of seeds Endosporic gametophytes o Grow and mature within the confines of the micro/megaspore wall o Produced by all heterosporous plants o Seed plant female gametophytes get help from previous generation to feed embryos Megasporangia – structures in which megaspores arise by meiosis o Not dispersed from parent plant o Megaspores stay in megasporangia, which stays attached to parent sporophyte plant o Sporophyte are large and photosynthetic; provide organic nutrients, minerals, and water to megaspores next is embryo sporophyte o Retention of megasporangia facilitates resource flow o Integument (covering) inhibits detachment Microsporangia – structures in which microspores arise by meiosis o Mature microspores with male gametophytes inside = pollen grains o Released to environment where they are dispersed by wind or other Pollination – transfer of pollen grains from microsporangia to ovules o Accomplished by wind o Droplet of liquid secreted by ovule dries and pulls pollen grain into micropyle toward egg germination: pollen tube grows from tip and releases sperm in vicinity of egg cells Fertilized egg cells make seeds o Integument becomes seed coat o Female gametophyte stores nutrients from sporophyte (before fertilization) – fill energy needs of developing embryo o Diploid embryo sporophyte at center, enveloped by haploid nutritional tissues, covered by protective seed coat of diploid sporophyte origin Darwin’s descent with modification o Ancestors of seed plants belonged to progymnosperms – secondary growth but no seeds; heterosporous (essential for origin of seeds) o Chances of outcrossing increased o Megaspore mother cell undergoes meiosis to produce 4 cells 1 becomes female gametophyte 23.4 Diversity of modern gymnosperms Pine life cycle Separate ovulate and pollen cones, can be on same tree or branch Microsporangia mature—pollen cones occur on lower branches in spring Ovulate cones occur on higher branches in spring to catch pollen from wind Immature pollen grains are dispersed Ovulate cones are immature; trap pollen grains AFTER pollination, megaspore is produced Pollen grain matures (2 sperm cells) Egg matures Fertilization Seed maturation Seed dispersal by wind Features Wood with no vessels (except Gnetum) but with tracheids and resin ducts Tracheids have tori (bordered pits) Resin forms amber when hardened Live in cold areas exposed to drought adaptations o Conical shape/flexible limbs allow snow shed o Pine needle shape and thick cuticle reduce water loss o Sunken stomata reduce exposure to wind o Walls of mesophyll have inward projections to add SA Chapter Wrap-up Examine and Discuss Self Test 1. What are the defining features of gymnosperms? 2. How do gymnosperms differ from pteridophytes such as ferns and bryophytes such as mosses? 3. Briefly describe how you would recognize a cycad, Ginkgo biloba, a conifer, and a gnetophyte. 4. Discuss the reproductive advantages of producing seeds, rather than exclusively spores. 5. Describe hypothetical steps in the origin of seeds. 6. Describe how humans use or otherwise value gymnosperms. Applying Concepts 1. Angiosperms are well known for their interactions with animals during reproduction. Are animals involved with pollination and seed dispersal in gymnosperms? If so, give some examples. How do gymnosperms accomplish pollination and seed dispersal without the aid of animals? 2. The roots of some gymnosperms grow up out of the ground into the air, and needles of some conifers fall off the tree at some times of the year. You might think that these features would be harmful to the plants, but they are not. Explain how natural selection generated these seemingly unfavorable traits. 3. Gymnosperms and angiosperms both produce structures characteristic of all seed plants, namely pollen, ovules, and seeds. How then do these two groups of seed plants differ in their reproduction?
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